1. Field of the Invention
This invention relates to a process for transforming, in a single stage, olefinically unsaturated omega-aldehydoacids into saturated omega-amino-acids. The industrial importance of these useful products is well known and requires no demonstration. It suffices to recall, for instance, the very widespread use of these aminoacids as monomers for the manufacture of polyamides employed as plastic materials or in the textile field, for the production of "nylon" fibers and yarns.
2. Description of the Prior Art
These omega-aminoacids are defined by the general formula H.sub.2 N--(CH.sub.2 --).sub.n+1 COOH wherein "n" is a whole number in the range from 4 to 16, and more commonly from 4 to 10.
The olefinically unsaturated omega-aldehydoacids have been disclosed by the publication of patent applications No. 74 24188 in France and Pat. No. P 24 33408 in the German Federal Republic by the applicant of this application. In said publications the methodology for obtaining such unsaturated aldehydoacids starting from cycloolefins comprising more than one ethylenic unsaturation, has also been described. Several omega-formyl-alkenoic acids, such as 11-formyl-4,8-undecadienoic acid, 7-formyl-4-heptenoic acid, 9-formyl-4-nonenoic acid and 9-formyl-6-nonenoic acid, with the respective production methodologies, had been described in the aforesaid publications.
In a more general form, the linear unsaturated aldehydoacids which can be used according to the present invention to obtain the desired saturated omega-aminoacids, may contain from 1 to 3 olefinic double bonds and correspond therefore to the general formula EQU O.dbd.CH--(CH.sub.2 --).sub.60 (CH.dbd.CH--).sub.92 (CH.sub.2 --).sub.62 (CH.dbd.CH--).sub.94 (CH.sub.2 --).sub.65 . . . (CH.dbd.CH--).sub.96 (CH.sub.2 --).sub.67 COOH (I)
wherein
.alpha.,.beta., .gamma., .delta. = whole numbers, equal or different from one another, chosen among 0,1,2 and 3; PA1 .rho., .sigma., .tau. = whole numbers, equal or different from one another, chosen among 0 and 1; PA1 (Examples: 7-formyl-4-heptenoic acid wherein .alpha. = 2, .beta. = 2, .gamma.= O, .delta. = 0, .rho. = 1, .sigma. = 0, n = 6; PA1 11-formyl-4,8-undecadienoic acid, wherein .alpha. = 2, .beta. = 2, .gamma. = 2, .delta. = 0, .rho. = 1, .tau. = 0, n = 10.) PA1 H'= an hydrogen atom of an acid compound; PA1 A = the residue of an acid compound; PA1 .alpha., .beta., .gamma., .sigma., .tau., .iota., .tau., n have the meanings specified hereinbefore. PA1 the hydrogen pressure for the hydrogenation is from 2 to 60 atmospheres: PA1 the duration of the hydrogenation is from 1 to 8 hours.
Provided that the following conditions are observed: EQU the sum .rho. + .sigma. + .tau. = 1,2 or 3; EQU the sum .alpha. + .beta. + .gamma. + .delta. + .rho. + .sigma. + .tau. = n
In the aforesaid patent publications the use of these unsaturated omega-aldehydoacids to obtain saturated omega-aminoacids had been contemplated. The methodology set forth in said publications for obtaining this result comprises a plurality of phases including two hydrogenation stages which are successive and clearly distinguished from one another.
The first of said stages consists in the reductive amination of an unsaturated .omega.-aldehydoacid to the corresponding unsaturated .omega.-aminoacid, characterized by the fact that the unsaturated .omega.-aldehydoacid is transformed by means of ammonia and an alkali metal hydroxide in aqueous solution, into the salt of the corresponding unsaturated iminoacid, which latter is hydrogenated in the presence of a catalyst under conditions which lead to the hydrogenation of the imino group. The second of these stages consists in the hydrogenation of the unsaturated .omega.-aminoacid thus obtained to the corresponding saturated aminoacid, characterized by the fact that the alkali salt of the unsaturated aminoacid is reacted with hydrogen in the presence of a second catalyst, in order to hydrogenate the olenifinc double bonds.
According to this previous methodology the hydrogenation catalyst of the first hydrogenation stage is preferably nickel, in the form of the metal or of salts thereof, pure or supported, or Raney nickel, whereas the second stage hydrogenation catalyst is preferably palladium in supported form. It had not been foreseen, nor was it in fact foreseeable in the light of the previous technical knowledge, that the two distinct hydrogenation stages could be conveniently substituted by a single stage using a single hydrogenation catalyst. Actually, if the catalyst employed for the hydrogenation of the imino groups were used under conditions (temperature above 150.degree. C) such as concurrently to catalyze the hydrogenation of the olefinic double bonds as well, one would obtain, beside the saturated .omega.-aminoacid, large quantities of undesired by-products, such as e.g. the corresponding secondary aminoacids, which are very harmful to the transformation of the .omega.-aminoacid to the corresponding polyamide as they would cause a cross-linking of the polyamide and the consequent lack of fusibility of the product. Likewise, if the catalyst for the hydrogenation of the olefinic double bonds (palladium) were concurrently used for the hydrogenation of the imino groups as well, one would equally obtain large amounts of secondary aminoacids as by-products, beside the .omega.-aminoacids.